Optical recording media is a digital storage media onto which patterns are marked and read by light, typically from a laser. Optical data recording media requires a grooved structure on which to place the recorded marks. The grooves, or “tracks” as they are referred to in optical recording, typically have sub-micron dimensions that are nearly impossible to see with standard optical microscopes. For example, grooves with about a 320 nanometer track pitch present the necessary surface features to a tracking servo system for its laser spot to lock onto while reading and writing data. The groove structure must have consistently high quality in order for the recording system to be reliable. One of the critical parameters for the grooves in optical tapes is that they remain tightly parallel to the edges of tape. Deviations from parallelism may occur if there are problems in the tape slitting process. Currently, there are no known instruments capable of simultaneously making an electronic image of both the groove pattern and the edges of optical tape.
FIGS. 1 and 2 illustrate a portion of a typical optical recording medium. FIG. 1 is a top view of an optical storage tape while FIG. 2 is a side view of an optical storage tape. Optical data storage tape 10 includes a nanostructure surface relief pattern embossed on surface 12 of the optical storage tape. The nanostructure includes bands 14 each of which include a plurality of tracks having lands 16 and grooves 18 embossed in the direction parallel to the face of optical data storage medium thereon in a preformatting process. Bands 14 are interposed between tape edges 20 and 22.
Optical tape has never been successfully commercialized so no known instruments exist for measuring groove pattern quality. Although certain diffractive based sensors do exist for the optical disk industry, this technology has never been extended to optical tapes.
Accordingly, there is a need for systems and method for accessing the parallelism in optical storage tapes.